Patent EA-001110-B1 (EA)
Title: Drilling system with means for anchoring in the borehole and methods of starting and ending drilling stroke using erd system
Inventor: BEST BRUNO
IPC: E21B47/18
Filed: 1998-08-19
Abstract: 1. An extended reach drilling (ERD) system for drilling a borehole in an underground formation, said ERD system comprising: a drill bit (11), a motor (10) for driving the drill bit (11), an elongate body (1) to surface, a hydraulic cylinder/piston arrangement (7, 9) for providing the required weight on bit, the elongate body (1) being coupled to a selected one of the cylinder (7) and the piston (9) of said cylinder/piston arrangement, the drill bit (11) being coupled to the other one of the cylinder (7) and the piston (9), and locking means (5,8) for locking said selected one of the cylinder (7) and the piston (9) against the borehole wall, the locking means (5,8) being operable between an engaged position and a disengaged position, characterized in that the elongate body is a drill string (1), and that the drill string (1) is coupled to said selected one of the cylinder (7) and piston (9) by swivel means (3) allowing rotation of the drill pipe (1) relative to said selected one of the cylinder (7) and the piston (9). 2. The ERD system of claim 1, wherein said selected one of the cylinder (7) and piston (9) is the cylinder (7), and said other one of the cylinder (7) and piston (9) is the piston (9). 3. The ERD system of claim 2, wherein said locking means comprises at least two sets of radially extendible locking members (5,8), the sets including a front set of locking members (8) being provided at a front part (at the bit side) of the cylinder (7) and a rear set of <DP=2locking members (5) being provided at a rear part (at the drill-pipe side) of the cylinder (7). 4. The ERD system of claim 3, wherein the locking members of at least one of the front set and the rear set of locking members (5,8) are capable of positioning the cylinder (7) concentric or eccentric in the borehole. 5. The ERD system of claim 4, wherein the front set of locking members (8) is capable of positioning said front part of the cylinder (7) concentric or eccentric in the borehole, and the rear set of locking members (5) is capable of positioning said rear part of the cylinder (7) concentric or eccentric in the borehole. 6. The ERD system of any one of claims 1-5, further comprising a hydraulic pump (4) for providing the power to operate the hydraulic cylinder/piston arrangement (7,9) for the drilling action and each locking member for the wall locking action, the hydraulic pump (4) being driven by rotation of the drill-pipe (1). 7. The ERD system of claim 6, wherein the motor (10) for driving the drill bit (11) is a hydraulic motor being driven by the oil from the hydraulic pump (4). 8. The ERD system of any one of claims 1-7, wherein the axial stroke of the cylinder/piston arrangement (7,9) is in the range of 1-5 metres. 9. The ERD system of any one of claims 1-8, further comprising inclinometers and magnetometers for carrying out directional measurements, being sent to surface via telemetry. 10. The ERD system of any one of claims 1-9, further comprising a memory to be entered by a pre-programmed well-path. 11. The ERD system of any one of claims 1-10, wherein the swivel means comprises a downhole clutch (3) which is operable between a disengaged position in which rotation of the drill-pipe (1) relative to said selected one of the cylinder (7) and the piston (9) is allowed, and an engaged position in which such relative rotation is prevented. 12. A method of starting a drilling stroke using the ERD system according to claim 11, the method comprising the following steps: a) the locking means (5, 8) being in its disengaged position, the piston (9) of the cylinder/piston arrangement (7,9) being in its retracted position; b) the drilling process is started as follows: c) the locking means (5, 8) is engaged thereby locking said selected one of the cylinder (7) and the piston (9) against the borehole wall; d) the cylinder/piston arrangement (7, 9) is actuated by which the drilling process is started, characterized in that in step a) mud is circulated at a reduced rate and the drill-pipe (1) is rotating relative to the cylinder/piston arrangement, in step b) the drilling process is started by full rate mud circulation, thereby triggering the downhole electronics, and in that before step c) the downhole clutch (3) is disengaged. 13. A method of ending a drilling stroke using the ERD system according to claim 11, comprising the following steps: a) the axial piston (9) is retracted; and  b) the locking means (5,8) is disengaged; characterized in that  c) the clutch (3) is engaged so that the whole system is rotating; d) a pressure pulse is sent to the surface to trigger the surface process;  e) the rotating string is lowered by a top-drive according to the piston stroke; f) mud circulation is reduced as a signal for the downhole electronics to monitor for full circulation to start the next drilling stroke.